Method and system for exhaust cleaning

Abstract

A method and a system for estimation of a soot load in a particle filter in an exhaust cleaning system, which estimation involves using a pressure drop across said particle filter in order to determine the soot load. Measurement of the pressure drop across the particle filter and therefore the estimation have to take place at a time when an exhaust mass flow of the exhaust cleaning system exceeds a flow threshold value, the particle filter is substantially free from water and a temperature of the particle filter exceeds a first threshold value. The result is a robust estimate of the soot load in the particle filter.

The invention claimed is: 
     
       1. A method for estimation of a soot load in a particle filter in an exhaust cleaning system, comprising:
 measuring a pressure drop across said particle filter to determine said soot load in said filter, wherein said estimation is based on said measuring of said pressure drop at a specific time when an exhaust volume flow of said exhaust cleaning system exceeds a flow threshold value; 
 determining whether said particle filter has for a sufficient period of time maintained a temperature above a second temperature threshold value which is high enough and for a sufficient period of time to remove water from said particle filter, so that said filter is substantially free from water; and 
 determining whether a temperature of said particle filter exceeds a first threshold value which is higher than a temperature at which water in exhaust gases in said exhaust cleaning system can condense. 
 
     
     
       2. A method according to  claim 1 , further comprising determining a magnitude of said exhaust volume flow based on an exhaust volume mass flow of said exhaust cleaning system, a pressure upstream of said exhaust volume from said particle filter and a temperature of said particle filter. 
     
     
       3. A method according to  claim 2 , further comprising:
 determining said pressure by means of a pressure sensor situated upstream in said exhaust volume flow from said particle filter; and 
 setting said flow threshold value at a high enough value selected to provide accuracy of said pressure sensor. 
 
     
     
       4. A method according to  claim 3 , wherein said flow threshold value corresponds to a flow of between 200 and 300 liters per second. 
     
     
       5. A method according to  claim 4 , wherein said flow threshold value corresponds to a flow of about 250 liters per second. 
     
     
       6. A method according to  claim 1 , further comprising determining whether said filter is substantially free from water by determining a water content in said particle filter by means of a model. 
     
     
       7. A method according to  claim 6 , wherein according to said model, said particle filter is substantially free from water if it has for at least a predetermined time been at a temperature above said second temperature threshold value. 
     
     
       8. A method according to  claim 7 , wherein said second threshold value exceeds a temperature at which water boils away out of pores in said particle filter. 
     
     
       9. A method according to  claim 8 , wherein said second threshold value corresponds to a temperature within the range 150-250° C. 
     
     
       10. A method according to  claim 8 , wherein said second threshold value corresponds to a temperature of about 200° C. 
     
     
       11. A method according to  claim 7 , wherein said predetermined time corresponds to a period of between 8 and 12 minutes. 
     
     
       12. A method according to  claim 7 , wherein said predetermined time corresponds to a period of about 10 minutes. 
     
     
       13. A method according to  claim 1 , wherein said first temperature threshold value depends on a temperature of said exhaust gases. 
     
     
       14. A method according to  claim 13 , wherein said first temperature threshold value corresponds to a temperature of between 140 and 200° C. 
     
     
       15. A method according to  claim 13 , wherein said first threshold value corresponds to a temperature of about 170° C. 
     
     
       16. A method according to  claim 1 , wherein when a value for said estimate is determined at said time, updating a previous value determined for said estimate is updated. 
     
     
       17. A method according to  claim 1 , wherein a signal corresponding to said estimate is filtered. 
     
     
       18. A system configured for estimating a soot load in a particle filter in an exhaust cleaning system, wherein the estimation uses a pressure drop across said particle filter to determine said soot load, said system comprising:
 a flow determining device configured to determine whether an exhaust volume flow of said exhaust cleaning system exceeds a flow threshold value; 
 a water presence determining device configured to determine if said particle filter is substantially free from water if said particle filter has for a sufficient period of time maintained a temperature above a second threshold value which is high enough to remove water from said particle filter; 
 a temperature estimating device configured to estimate a temperature of said particle filter; and 
 an estimator device configured for effecting said soot load estimation on the basis of a measurement of said pressure drop made at a specific time when said exhaust mass volume flow exceeds a flow threshold value, said particle filter is substantially free from water and said temperature of said particle filter exceeds a first threshold value which is higher than a temperature at which water in exhaust gases in said exhaust cleaning system can condense. 
 
     
     
       19. A vehicle comprising:
 a particle filter; and 
 a system for estimating a soot load in said particle filter according to  claim 18 . 
 
     
     
       20. A computer program product pertaining to a system for estimating a soot load in a particle filter wherein said program product comprises a non-transitory computer-readable medium and a computer program stored on said medium; said computer program comprising program code with program instructions for causing a computer to cause performance of the steps of the method according to  claim 1 . 
     
     
       21. The computer program product of  claim 20 , wherein said program code is contained in said medium which takes the form of any from among ROM (read-only memory), PROM (programmable ROM), EPROM (erasable PROM), flash-memory, EEPROM (electrically EPROM) and hard disc unit. 
     
     
       22. The method of  claim 1 , wherein said temperature of said particle filter is determined by at least one temperature sensor positioned proximal to said particle filter configured to measure the temperature of said particle filter.